John Lightfoot on Matthew 17:4

[Let us make here three tabernacles, &c.] The transfiguration of Christ was by night. Compare Luke 9:37. The form of his face and garments is changed while he prays; and Moses and Elias come and discourse with him concerning his death (it is uncertain how long), while as yet the disciples that were present were overcharged with sleep. When they awaked, O what a spectacle had they! being afraid, they observe and contemplate, they discover the prophets: whom, now departing, Peter would detain; and being loath that so noble a scene should be dispersed, made this proposition, "Let us make here three tabernacles," &c. Whence he should know them to be prophets, it is in vain to seek, because it is nowhere to be found; but being known, he was loath they should depart thence, being ravished with the sweetness of such society, however astonished at the terror of the glory; and hence those words, which when he spake he is said by Luke "not to know what he said"; and by Mark, "not to know what he should say"; which are rather to be understood of the misapplication of his words, than of the sense of the words. He knew well enough that he said these words, and he knew as well for what reason he said them; but yet "he knew not what he said"; that is, he was much mistaken when he spake these words, while he believed that Christ, Moses, and Elias, would abide and dwell there together in earthly tabernacles.